The present invention relates to an electrode and associated capacitor structure for a semiconductor device, and more particularly to provision of a thin, oxygen-annealed, electrically conductive barrier layer adjacent a dielectric as part of the electrode.
A known capacitor includes two electrodes sandwiching a dielectric. A capacitance value of the capacitor characterizes an amount of charge that would be collected at the electrodes for a given applied voltage between the electrodes. This capacitance value is expressed by the equation EQU C=.epsilon..sub.r.epsilon..sub.o A/d
wherein
.epsilon..sub.r =the relative dielectric constant of the dielectric between electrodes, PA1 .epsilon..sub.o =the permittivity of free space, PA1 A=the surface area of the electrodes sandwiching the dielectric material, and PA1 d=the distance between the electrodes.
The capacitance value (C) of the capacitor is directly proportional to an area (A) of opposing surfaces of the electrodes, directly proportional to a relative dielectric constant (.epsilon..sub.r) of the dielectric, and inversely proportional to the distance (d) between the electrodes.
An ideal capacitor, once charged by a given applied voltage, would hold its collected charge for an infinite duration--i.e., permitting no leakage current through the dielectric between the electrodes. Such ideal capacitor would also tolerate large voltage applications. However, it is known that certain physical limitations of real-world materials restrict the availability of such an ideal capacitor.
Known dielectrics exhibit voltage breakdown characteristics, wherein the influence of a sufficiently large electric field causes a breakdown within the dielectric material. Accordingly, for a given voltage application, a minimum distance or dielectric thickness is maintained between electrodes in order to avoid short-circuit failures by way of the dielectric's electric-field breakdown. Per the above equation, this requirement of a minimum distance between electrodes, therefore, limits the magnitude of the available capacitance value for a given electrode area
Furthermore, the known dielectrics currently are not capable of blocking all current leakage, but instead have a finite conductivity (i.e., less than infinite resistance). Thus, a finite leakage current passes through the dielectric, which can deplete collected charge of the capacitor over a given period of time. As a result, when the capacitor is employed in a memory integrated circuit, e.g., a dynamic random access memory device, the capacitor requires a periodic refresh in order to restore the capacitor's charge before it is depleted. Preferably low, the refresh frequency for a memory device is governed by the charge retention capabilities of the capacitor and the amount of charge that it is able to collect--which parameters/qualities, in-turn, are proportional to capacitance value the capacitor and its applied voltage, respectively.
As inferred above, memory integrated circuits (e.g., a dynamic random access memory semiconductor devices) commonly employ capacitor elements. Manufacturers of these components continually push to shrink device geometries as a part of reducing manufacturing costs. However, given that the capacitance of a capacitor is directly proportional to the area of its electrode plates, a technical compromise exists between (i) the desire to reduce device geometry, and (ii) the need to maintain, or increase, charge retention of the capacitor for improving the performance of associated memory devices.
Embodiments of the present invention provide new electrode and capacitor structures, and methods of fabrication thereof, which overcome at least some of the above limitations and trade-offs.